<!DOCTYPE html>
<html>
<head>
<style type="text/css">
#abs {
 position: absolute;
 left: 20px; top: 20px;
 width: 100px;
 background-color: red;
}
#parent {
 margin-bottom: 70px;
}
#zero-height {
 margin-bottom: 100px;
 height: 0;
}
#child-of-zero-height {
 height: 100px; background: green;
}
</style>
</head>
<body>
<div id="abs">
 <div id="parent">
  <div id="zero-height">
   <div id="child-of-zero-height"></div>
  </div>
 </div>
</div>
</body>
</html>
